port = CreateObject("roMessagePort")
screen = CreateObject("roVideoScreen")
By default it is enabled - so there isn't any reason to specify that unless you want to disable it - and using the feature locks your channel to run on devices with firmware 5.2 or higher.
Unless you want to disable it you should remove the line so it will still work on older devices.
It's probably not working because you don't have the sdbifurl/hdbifurl metadata used by trickplay.
SDBifUrl-String-URL for SD Trick Modes-http://www.myco.com/bif/sd1932.bif
HDBifUrl-String-URL for HD Trick Modes-http://www.myco.com/bif/hd1932.bif
http://sdkdocs.roku.com/display/sdkdoc/ ... cification